CN211202110U

CN211202110U - Turbocharger turbine diffuser with deswirl ribs

Info

Publication number: CN211202110U
Application number: CN201921539963.3U
Authority: CN
Inventors: D·G·格拉博斯卡
Original assignee: BorgWarner Inc
Current assignee: BorgWarner Inc
Priority date: 2018-09-13
Filing date: 2019-09-16
Publication date: 2020-08-07
Anticipated expiration: 2029-09-16
Also published as: EP3623590A2; US10422344B1; EP3623590A3; EP3623590B1; CN110894807B; CN110894807A

Abstract

The present disclosure provides a turbocharger turbine diffuser having deswirl ribs. A turbine diffuser configured for use with a turbocharger is disclosed. The turbine diffuser may include: a diffuser wall defining a diffuser and surrounding a central axis of the diffuser; and a plurality of deswirl ribs, each extending axially along the diffuser wall. Each de-swirl rib may have a first end attached to the diffuser wall and an opposite second end exposed in the interior space of the diffuser. The de-swirl rib may be configured to reduce rotation of exhaust gas flowing through the diffuser.

Description

Turbocharger turbine diffuser with deswirl ribs

Technical Field

The present disclosure relates generally to turbochargers and, more particularly, to turbocharger turbine diffusers having a swirl-relieved rib for reducing the rotation of the exhaust flow.

Background

Vehicle engine systems may include a turbocharger that uses exhaust gas flow to increase boost pressure of intake air supplied to the engine. Specifically, a turbocharger may have a compressor section with a compressor wheel, and a turbine section with a turbine wheel and a diffuser downstream of the turbine wheel. The exhaust flow through the turbine section may rotate the turbine wheel and drive the compressor wheel to rotate via the interconnecting shaft. The rotating compressor wheel may pressurize intake air supplied to the engine through an intake manifold.

At the design point of the turbine section, the exhaust gas flow exits the turbine wheel with little or no swirl/rotation relative to the turbine housing. The design point represents the mass flow rate that produces the peak operating efficiency of the turbine section at a given speed. When the mass flow deviates from the design point, the turbine section is considered to be operating at an off-design condition, where the exhaust flow exiting the turbine wheel exhibits rotation relative to the turbine housing. The swirling or rotating exhaust flow exiting the turbine wheel under off-design conditions may move radially outward toward the limits of the diffuser due to conservation of angular momentum.

Many diesel engine systems include an aftertreatment system in the exhaust to remove or reduce the level of certain pollutants in the exhaust stream. Such aftertreatment systems use various catalysts that selectively convert target pollutants in the exhaust gas flow. Increasingly, engine manufacturers locate aftertreatment catalysts, such as Diesel Oxidation Catalysts (DOCs), closer to the exhaust of the turbine section. For example, the DOC catalyst may be placed immediately downstream of the downstream end of the turbine diffuser, or may even protrude into the turbine diffuser. This arrangement advantageously provides the catalyst with a high temperature exhaust gas as the gases exit the turbine wheel, promoting catalyst light-off and catalytic conversion of target pollutants in the exhaust stream. However, under off-design conditions, the swirling/spinning exhaust gas may move radially outward toward the outer edge of the catalyst. Therefore, under non-design conditions, the exhaust gas may be unevenly distributed on the surface of the catalyst, resulting in a decrease in catalytic efficiency.

U.S. patent application No.2016/0245119 discloses a turbocharger diffuser having a center body within the diffuser supported by de-swirl vanes extending from the wall of the diffuser. The center body and the de-swirl vanes create a de-swirl passage for exhaust gas flowing through the diffuser. While effective, this document does not mention the use of a de-swirl channel to promote uniform distribution of the exhaust stream over the surface of the downstream aftertreatment catalyst.

Therefore, a strategy is needed to improve the uniformity of exhaust flow of an aftertreatment catalyst located near the turbine section discharge.

SUMMERY OF THE UTILITY MODEL

According to one aspect of the present disclosure, a turbine diffuser configured for use with a turbocharger is disclosed. The turbine diffuser may include a diffuser wall defining the diffuser and surrounding a central axis of the diffuser. The turbine diffuser may also include a plurality of deswirl ribs, each extending axially along the diffuser wall. Each de-swirl rib may have a first end attached to the diffuser wall and an opposite second end exposed in the interior space of the diffuser. The de-swirl rib may be configured to reduce rotation of exhaust gas flowing through the diffuser.

In accordance with another aspect of the present disclosure, a turbocharger for an engine system is disclosed. The engine system may have an exhaust pipe with an aftertreatment catalyst for treating exhaust gas produced by the engine system. The turbocharger may include a compressor section and a turbine section rotatably coupled to the compressor section by a shaft. The turbine section may include a turbine wheel and a diffuser downstream of the turbine wheel. The diffuser may be defined by a diffuser wall extending circumferentially about a central axis of the diffuser and surrounding an interior space of the diffuser. The turbocharger may also include a plurality of deswirl ribs extending axially along the diffuser wall. Each de-swirl rib may have a first end attached to the diffuser wall and an opposite second end exposed for contact with exhaust gas flowing through the interior space of the diffuser. The de-swirl rib may be configured to reduce the tangential velocity of the exhaust gas flowing through the diffuser.

In accordance with another aspect of the present disclosure, a method for providing an evenly distributed exhaust gas flow to an aftertreatment catalyst of an engine system having a turbocharger is disclosed. The aftertreatment catalyst may be positioned adjacent a downstream end of a turbine diffuser of the turbocharger. The method may include providing a plurality of deswirl ribs extending axially along a diffuser wall of the diffuser. Each de-swirl rib may have a first end attached to the diffuser wall and an opposite second end exposed in the interior space of the diffuser. The method may further comprise: if the exhaust gas is rotating, the deswirl ribs are used to straighten the exhaust gas flow through the diffuser and allow the straightened exhaust gas flow to the aftertreatment catalyst.

These and other aspects and features of the present disclosure will be more readily understood when read in conjunction with the appended drawings.

Drawings

FIG. 1 is a schematic illustration of a vehicle engine system having a turbocharger with a turbine section and an aftertreatment catalyst located near or at an exhaust of the turbine section constructed according to the present disclosure.

FIG. 2 is a cross-sectional view through a portion of the turbine section of the turbocharger of FIG. 1, illustrating deswirl ribs in the diffuser of the turbine section constructed in accordance with the present disclosure.

FIG. 3 is an end view of the diffuser as viewed from direction 3 of FIG. 2 constructed in accordance with the present disclosure.

FIG. 4 is an end view similar to FIG. 3, but with the de-swirl ribs constructed according to the present disclosure angled relative to the diffuser wall.

FIG. 5 is a cross-sectional view of a turbine section similar to FIG. 2, but with the height of the deswirl ribs constructed according to the present disclosure being constant along the length of the diffuser.

FIG. 6 is a cross-sectional view of a turbine section similar to FIG. 2, but with a deswirl rib constructed according to the present disclosure having a different starting point along the diffuser wall.

FIG. 7 is a cross-sectional view of a turbine section similar to FIG. 6, but with a de-swirl rib constructed according to the present disclosure having a different starting point and a different ending point along the diffuser wall.

FIG. 8 is a sectional view of a turbine section similar to FIG. 2, but with a de-swirl rib constructed in accordance with the present disclosure having a T-shaped cross-section.

FIG. 9 is a schematic illustration of the effect of a T-shaped de-swirl rib constructed according to the present disclosure on a rotating exhaust stream.

FIG. 10 is a cross-sectional view of a turbine section similar to FIG. 2, but with one de-swirl rib constructed in accordance with the present disclosure having mounting structure for mounting a nitrogen oxide (NOx) sensor.

FIG. 11 is a cross-sectional view of a turbine section similar to FIG. 10, but with a NOx sensor constructed according to the present disclosure mounted on the deswirl rib.

FIG. 12 is a flow chart of a series of steps that may be involved in providing uniform distribution of exhaust flow over the surface of an aftertreatment catalyst according to a method of the present disclosure.

Detailed Description

Referring now to the drawings, and in particular to FIG. 1, an exemplary engine system 10 is illustrated. The engine system 10 may be installed in a vehicle, or it may be used in stationary applications (e.g., generator sets). The engine system 10 includes a diesel engine 12, the diesel engine 12 having an intake manifold 14 to supply intake air 15 to combustion chambers of the engine 12 for combustion. The engine system 10 also includes an exhaust manifold 16 that directs exhaust gases produced in the engine 12 to a turbocharger 18. The turbocharger 18 uses the exhaust flow to increase the boost pressure of the intake air 15 supplied to the engine 12, increasing the power density of the engine by allowing more fuel to burn. Optionally, the engine system 10 may also include an Exhaust Gas Recirculation (EGR) system 20 for recirculating exhaust gas back to the engine 12 via a recirculation line 21 to reduce combustion temperatures and the formation of nitrogen oxides (NOx) in the engine 12.

The turbocharger 18 includes a compressor section 22 having a compressor wheel 24 and a turbine section 26 having a turbine wheel 28. A shaft 30 rotatably connects the compressor wheel 24 and the turbine wheel 28. The exhaust flow passes through the turbine section 26, causing the turbine wheel 28 to rotate, thereby driving rotation of the compressor wheel 24 via the interconnecting shaft 30. The rotating compressor wheel 24 pressurizes intake air 15, which is supplied to the engine 12 through the intake manifold 14. The pressurized intake air 15 has a higher density for a given volume than air at atmospheric pressure. Thus, more fuel may be added to the pressurized intake air 15 at a given air/fuel ratio, and more power and torque may be generated by combusting a greater amount of fuel.

An aftertreatment catalyst 32, such as a Diesel Oxidation Catalyst (DOC)34, may be located at or near the exhaust of the turbine section 26 to catalytically convert one or more pollutants in the exhaust flow before the exhaust is released to the environment through an exhaust pipe 36. Although not shown in FIG. 1, it should be understood that the engine system 10 may have an additional aftertreatment catalyst in the exhaust pipe 36 to reduce the level of pollutants in the exhaust gas stream.

The structure of the turbine section 26 is shown in more detail in FIG. 2. The turbine section 26 includes a diffuser 38 downstream of the turbine wheel 28 and defined by a diffuser wall 40, the diffuser wall 40 surrounding a central axis 42 of the diffuser 38. Diffuser wall 40 circumferentially surrounds and defines an interior space 44 of diffuser 38, with exhaust gas exiting turbine wheel 28 flowing through diffuser 38 before entering exhaust pipe 36. The diffuser wall 40 extends axially from an upstream end 46 to a downstream end 48, and the aftertreatment catalyst 32 may be positioned in the exhaust pipe 36 adjacent the downstream end 48 of the diffuser 38 (see also fig. 5). However, in some cases, the aftertreatment catalyst 32 may protrude into the interior space 44 of the diffuser 38. The diffuser wall 40 may be angled such that the cross-sectional area of the diffuser 38 increases from the upstream end 46 to the downstream end 48.

The diffuser 38 includes a plurality of deswirl ribs 50 extending axially along the diffuser wall 40. The diffuser 38 may have from 2 to about 30 de-swirl ribs 50, depending upon various design considerations, although in some cases the diffuser 38 may have more than 30 de-swirl ribs 50. The de-swirl ribs 50 are configured to reduce the rotation of the rotating exhaust flow 52 flowing through the diffuser 38 under off-design conditions. FIG. 2 depicts the swirling exhaust flow 52 being straightened when it impinges on a deswirl rib 50 under off-design conditions. Specifically, the rotating exhaust flow 52 impinges on the flanks 54 of the de-swirl ribs 50, thereby reducing the tangential velocity of the rotating flow. The straightening of the exhaust flow prevents the exhaust from moving radially outward to the outer boundary of diffuser wall 40 and being distributed primarily around the outer edge of aftertreatment catalyst 32. The straightened flow of exhaust gas is more evenly distributed over the surface of the aftertreatment catalyst 32 to improve catalytic efficiency. However, when the turbine section 26 is operating at a design point and the exhaust flows axially (not rotating), the de-swirl ribs 50 may have little or no effect on the flow direction of the exhaust and may maintain a non-rotating flow.

The deswirl ribs 50 may be evenly spaced around the inner circumference of the diffuser wall 40 with equal angular spacing between the ribs 50. In other arrangements, the de-swirl ribs 50 may be asymmetrically distributed with varying angular spacing between the de-swirl ribs 50. Each deswirl rib 50 may have an axial length (i) beginning at an upstream starting point 56 and ending at a downstream ending point 58, and the starting point 56 and ending point 58 of the rib 50 may be located at different positions along the diffuser wall 40 in various designs of the diffuser 38. For example, although FIG. 2 depicts the terminus 58 of the deswirl rib 50 being flush with the downstream end 48 of the diffuser 38, the deswirl rib 50 may terminate at a more upstream location in alternative designs of the diffuser 38 (see further discussion below).

Each deswirl rib 50 has a radially outward first end 60 attached to the diffuser wall 40 and an opposite radially inward second end 62, the second ends 62 being exposed in the interior space 44 of the diffuser 38 for contact with exhaust gas flowing therethrough. The deswirl ribs 50 may be integrally formed with the diffuser wall 40, or they may be attached thereto by welding or other suitable attachment method. The deswirl rib 50 is connected to the diffuser wall 40 only at a first end 60 radially outward and is not attached to any other structure within the diffuser 38. Specifically, the de-swirl ribs 50 are small pieces that extend axially along the diffuser wall 40 and do not protrude too far into the discharge of the turbine wheel 28. The deswirl ribs 50 do not cross the diffuser 38 and do not approach the central axis 42. It is believed that this arrangement may enhance the stability of the de-swirl rib 50 in the high vibration environment of the turbine diffuser 38 while also minimizing pressure waves reflected from the de-swirl rib 50 that may impinge on the turbine wheel 28 and cause undesirable vibrations at the turbine wheel 28.

Each deswirl rib 50 has a height (h) measured from a first end 60 radially outward to a second end 62 radially inward. As shown in fig. 2, the height (h) of the deswirl rib 50 increases along the length of the diffuser wall 40 such that the deswirl rib 50 becomes progressively higher downstream along the diffuser wall 40. The higher portion of the de-swirl rib 50 may more effectively prevent the flow of exhaust gas from passing over the rib 50 and bypassing the straightening effect of the rib 50. Further, the length (l) of the deswirl rib 50 may be shorter than or equal to the axial length of the diffuser 38. In the axial direction, the deswirl rib 50 may extend parallel to the central axis 42 of the diffuser 38, as shown, although in alternative arrangements, the deswirl rib 50 may be angled or curved relative to the central axis 42.

Turning now to fig. 3, the deswirl rib 50 may extend radially inward toward the central axis 42 such that the deswirl rib 50 is perpendicular to the diffuser wall 40 and the second radially inward end 62 is directed toward the central axis 42. Alternatively, as shown in FIG. 4, the deswirl ribs 50 may be angled or inclined relative to the diffuser wall 40 such that the radially inward second ends 62 are not directed directly toward the central axis 42. If inclined or angled with respect to the diffuser wall 40, the deswirl ribs 50 may all be angled in the same direction as shown.

In an alternative arrangement, the height (h) of the deswirl ribs 50 may be constant along the length of the diffuser wall 40, as shown in fig. 5. In addition, the deswirl ribs 50 may have different lengths (l) in the axial direction, as shown in FIGS. 6-7. For example, the starting points 56 of the deswirl ribs 50 may be positioned at various axial locations along the diffuser wall 40 (see FIG. 6). Alternatively, both the start point 56 and the end point 58 of the deswirl rib 50 may be located at various axial positions along the diffuser wall 40 (see FIG. 7).

The deswirl rib 50 of fig. 2-7 has a rectangular cross-section. In another embodiment, diffuser wall 40 has a de-swirl rib 70 that is T-shaped in cross-section, as shown in FIGS. 8-9. Specifically, each T-shaped de-swirl rib 70 has a radially extending stem 72, the stem 72 being covered at the radially inward second end 62 by a lateral cross-bar 74. The cross-bar 74 may prevent or block the rotating exhaust flow 52 from passing over the de-swirl ribs 70 and may more aggressively reduce the tangential velocity of the flow 52. As shown in fig. 8-9, the rotating exhaust flow 52 may impinge on the sides 76 of the radially extending rods 72 and/or the lower lip 78 of the cross-bar 74, the lower lip 78 preventing the exhaust flow from passing over the ribs 50. The impingement of the exhaust flow 52 on the side face 76 and/or the lower lip 78 may create turbulence in the flow, which helps to direct the flow in an axial direction. The cross-bar 74 may extend along the entire axial length (l) of the deswirl rib 70 (see fig. 8). Further, the height of the T-shaped deswirl ribs 70 may increase gradually along the length of the diffuser 38, as shown in FIG. 8, although the height may also be constant along the length of the diffuser 38. In addition, as described above with reference to fig. 2-7, the T-shaped deswirl rib 70 may extend parallel to the central axis 42 of the diffuser 38 or may be angled or curved relative to the central axis 42. The T-shaped deswirl ribs 70 may have the same or varying axial lengths relative to each other, and the number and angular spacing of the T-shaped deswirl ribs 70 may vary according to various design considerations.

In an alternative embodiment, one or more of the deswirl ribs 50 (or the T-shaped deswirl ribs 70) include a mounting structure 80 for mounting a NOx sensor 82 (see fig. 10-11). Mounting structure 80 may be a boss 84 welded or otherwise secured to de-swirl rib 50 that facilitates mounting NOx sensor 82 to de-swirl rib 50. Alternatively, mounting structure 80 may be other types of structures that facilitate mounting NOx sensor 82, such as, but not limited to, fasteners, fastener receivers, or protruding features. The NOx sensor 82 may be exposed on the surface of the deswirl rib 50 to facilitate exposure of the NOx sensor 82 to the exhaust gas exiting the turbine wheel 28. In some arrangements, the NOx sensor 82 may be embedded or partially embedded in the de-swirl rib 50 such that the NOx sensor 82 is positioned internally within the de-swirl rib 50.

Mounting NOx sensor 82 to de-swirl rib 50 provides several advantages over placing NOx sensor 82 on diffuser wall 40 in current systems. The NOx sensor 82 on the de-swirl rib 50 may be more exposed to the exhaust gas as it exits the turbine wheel 28 at design points and off-design conditions. In contrast, prior art diffuser wall mounted NOx sensors may be exposed to the recirculated exhaust gas flow when the turbomachine is operating at the design point. The placement of the NOx sensor 82 on the deswirl rib 50 positions the NOx sensor 82 slightly deeper into the exhaust gas flow to enhance NOx detection in the exhaust gas as it exits the turbine wheel 28. The deswirl rib 50 may also support the structural stability of the NOx sensor 82 in the high vibration environment of the diffuser 38.

INDUSTRIAL APPLICABILITY

In general, the teachings of the present disclosure may find applicability in many industries, including but not limited to the automotive industry. For example, the teachings of the present disclosure may be applicable to industries that use engine systems having a turbocharger and an aftertreatment catalyst located at or near the exhaust of the turbine section of the turbocharger.

FIG. 12 is a flow chart showing a series of steps that may be involved in providing an even distribution of exhaust flow over the face of aftertreatment catalyst 32 according to the present disclosure. As shown, these steps may vary depending on whether the turbine section 26 is operating at a design point or under non-design conditions. If the turbine section 26 is operating at off-design conditions, the rotating exhaust flow may be discharged from the turbine wheel 28 into the diffuser 38 according to block 100. The rotating exhaust flow may then be straightened (or at least partially straightened) to a non-rotating axial flow as the rotating exhaust gas strikes the deswirl rib 50 (or the T-shaped deswirl rib 70) along the diffuser wall 40 (block 102). However, if the turbine section 26 is operating at the design point, the exhaust flow discharged from the turbine wheel 28 may flow axially and may be non-rotating (block 104) such that the

de-swirl ribs

50 or 70 do not affect the exhaust flow direction (block 106). Thus, at design point conditions or non-design conditions, substantially straight or non-rotating exhaust gas may be provided to the aftertreatment catalyst 32, as per block 108. Accordingly, uniform distribution of exhaust gas over the face of the aftertreatment catalyst 32 is achieved both at design points and under off-design conditions to support the catalytic efficiency of the catalyst 32 (block 110). This is an advantage over prior art systems where the aftertreatment catalyst is located at or near the downstream end of the diffuser and where even distribution of exhaust gas over the face of the catalyst is achieved only when the turbine is operating at design point conditions.

The present disclosure provides a plurality of deswirl ribs along a diffuser wall of a turbine diffuser as a flow straightener for exhaust gas discharged from a turbine wheel. The de-swirl ribs may reduce the tangential velocity of the exhaust gas as it spins under off-design conditions, but may have little or no effect on the non-spinning exhaust flow under design point conditions. When the rotating exhaust gas impinges on the deswirl ribs, turbulence may be created in the flow and the flow is directed axially. In some embodiments, the de-swirl ribs may have a T-shape with crossbars that may help capture the rotating exhaust gas to prevent the straightening effect of the exhaust gas around the de-swirl ribs. Thus, a non-rotating exhaust stream is provided to the aftertreatment catalyst at both design points and non-design conditions. The non-rotating exhaust flow is more evenly distributed over the surface of the catalyst to increase catalytic efficiency. This is an improvement over prior art systems in which the rotating exhaust gas flows primarily to the outer edge of the catalyst under off-design conditions.

In addition, a deswirl rib may provide a location for mounting a NOx sensor in a turbine diffuser. Mounting the NOx sensor on the deswirl rib rather than directly on the diffuser wall as in the prior art, more advantageously positions the NOx sensor exposed to the exhaust gas as it is discharged from the turbine wheel at both design points and off-design conditions. In addition, the deswirl ribbed structure may support the NOx sensor in the high vibration environment of the turbine diffuser, thereby reducing the possibility of vibration and cracking at the sensor.

Claims

1. A turbo diffuser configured for use with a turbocharger, comprising:

a diffuser wall defining the diffuser and surrounding a central axis of the diffuser, wherein the diffuser wall is angled relative to the central axis of the diffuser such that a cross-sectional area of the diffuser increases as the diffuser wall extends from an upstream end proximate to a turbine wheel of the turbocharger to a downstream end opposite the turbine wheel; and

a plurality of de-swirl ribs, each de-swirl rib extending axially along the diffuser wall, each de-swirl rib having a first end attached to the diffuser wall and an opposite second end exposed in the interior space of the diffuser, the de-swirl ribs configured to reduce rotation of exhaust gas flowing through the diffuser.

2. The turbine diffuser of claim 1, wherein the deswirl rib is rectangular in cross-section.

3. The turbine diffuser of claim 1, wherein each of the de-swirl ribs is T-shaped in cross-section.

4. The turbine diffuser of claim 1, wherein the height of each deswirl rib increases gradually along the length of the diffuser wall.

5. The turbine diffuser of claim 1, wherein a height of each of the de-swirl ribs is constant along a length of the diffuser wall.

6. The turbine diffuser of claim 1, wherein one of the de-swirl ribs includes a mounting structure configured to facilitate mounting of a nitrogen oxide sensor to the de-swirl rib.

7. The turbine diffuser of claim 1, wherein each of the de-swirl ribs extends radially inward from the diffuser wall toward the central axis.

8. The turbine diffuser of claim 1, wherein the de-swirl ribs have different axial lengths.

9. The turbine diffuser of claim 1, wherein the turbine diffuser includes 2 to 30 of the deswirl ribs along the diffuser wall.

10. A turbocharger for an engine system having an exhaust pipe with an aftertreatment catalyst for treating the exhaust gas, the turbocharger comprising:

a compressor section;

a turbine section rotatably coupled to the compressor section by a shaft, the turbine section including a turbine wheel and a diffuser downstream of the turbine wheel, the diffuser being defined by a diffuser wall extending circumferentially about a central axis of the diffuser and surrounding an interior space of the diffuser, wherein the diffuser wall is angled relative to the central axis of the diffuser such that a cross-sectional area of the diffuser increases as the diffuser wall extends from an upstream end proximate the turbine wheel to a downstream end opposite the turbine wheel; and

a plurality of de-swirl ribs, each de-swirl rib extending axially along the diffuser wall, each de-swirl rib having a first end attached to the diffuser wall and an opposite second end exposed to contact exhaust gas flowing through the interior space of the diffuser, the de-swirl ribs configured to reduce tangential velocity of exhaust gas flowing through the interior space of the diffuser.

11. The turbocharger of claim 10, wherein the deswirl rib is attached only to the diffuser wall and not to any other structure in the interior space of the diffuser.

12. The turbocharger of claim 10, wherein the downstream end is adjacent the aftertreatment catalyst when the turbocharger is installed in the engine system.

13. The turbocharger of claim 10, wherein the deswirl rib is rectangular in cross-section.

14. The turbocharger of claim 10 wherein each of the de-swirl ribs is T-shaped in cross-section.

15. The turbocharger of claim 10, wherein a height of each deswirl rib is constant along a length of the diffuser wall.

16. The turbocharger of claim 10, wherein the height of each deswirl rib increases gradually along the length of the diffuser wall.

17. The turbocharger of claim 10, wherein one of the de-swirl ribs includes a mounting structure for mounting a nitrogen oxide sensor to the de-swirl rib.